Positive photoresists containing an alkali-soluble resin and a photosensitizer such as 1,2-naphthoquinone diazide are known as resists for use in, for example, the manufacture of semiconductor devices such as ICs and LSIs, the manufacture of displays such as LCDs, and the manufacture of printing plates. One proposed positive photoresist composition contains a cresol novolac resin prepared from m-cresol and p-cresol as an alkali-soluble resin (see, for example, PTL 1).
Also proposed is a positive photoresist composition containing a cresol novolac resin prepared from m-cresol, p-cresol, and resorcinol as an alkali-soluble resin (see, for example, PTL 2).
Whereas the positive photoresist compositions disclosed in PTLs 1 and 2 are developed to provide high developability, e.g., high sensitivity, there is a need for a higher sensitivity because finer patterns have been used with the increasing packing density of semiconductor devices in recent years. Unfortunately, the positive photoresist composition disclosed in PTL 1 has insufficient sensitivity for use in forming such finer patterns. A need also exists for a higher heat resistance because semiconductor manufacturing processes, for example, involve various heat treatments. Unfortunately, the positive photoresist composition disclosed in PTL 1 has insufficient heat resistance.
One problem is that a novolac phenolic resin, which is an alkali-soluble resin, designed to have a higher alkali solubility so that it has a higher sensitivity exhibits a lower heat resistance, whereas a novolac phenolic resin designed to have a higher heat resistance exhibits a lower sensitivity, and this makes it difficult to achieve high sensitivity and high heat resistance at the same time. Accordingly, there is a need for a material that has high sensitivity and high heat resistance at the same time.